1. Field of the Invention
The present invention relates to a microcellular polyurethane elastomer and a method of producing the same, more particularly to a microcellular polyurethane elastomer for a shoe sole and a method of producing the same.
2. Description of the Prior Art
A microcellular polyurethane elastomer has fine cells uniformly dispersed in a formed body, and is characterized by its forming density lower than that of a solid type polyurethane elastomer but higher than that of a flexible polyurethane foam. The microcellular polyurethane elastomer has been used for, e.g., shoe soles, gaskets, sealants and vibration insulators, and is still a very important material.
The representative microcellular polyurethane elastomer is produced by reacting a resin premix with an isocyanate component, wherein the resin premix is a mixture of a polyol component and one or more aids/additives, e.g., chain extender, catalyst, foam stabilizer and foaming agent.
It is known that polyester polyol and polyoxyalkylene polyol are used as the polyol component.
However, the microcellular polyurethane elastomer using a polyester polyol is insufficient in resistance to hydrolysis, although excellent in various physical properties, e.g., tensile strength, elongation and tear strength. Therefore, various attempts have been done to retard the hydrolysis, e.g., use of various types of additives and modification of chemical structures of polyester polyol. One of the methods proposed so far for improving resistance to the hydrolysis is to contain 0.001 to 0.007 mol of a compound having 3 active hydrogen atoms per 1000 g of the polyurethane resin produced, to cause a small quantity of branched structure. Such a compound, however, is still required to be further improved in resistance to hydrolysis.
On the other hand, use of polyoxypropylene polyol as the polyoxyalkylene polyol is known to improve resistance of the polyurethane to hydrolysis. However, a polyoxypropylene polyol has generally insufficient reactivity, and causes problems, e.g., extended demolding time and deterioration of green and final strength. These problems may be solved by increasing quantity of the catalyst, which, however, is accompanied by other problems, e.g., deterioration of processability and moldability resulting from shortened cream time or gel time.
Development of a polyoxyalkylene polyol exhibiting higher physical characteristics has been demanded even for the areas to which the conventional polyoxyalkylene polyol is sufficiently applicable with its resistance to hydrolysis, because of the problems associated with production of the polyol. One of the methods generally used for producing a polyoxyalkylene polyol is addition polymerization in which an active hydrogen compound is reacted with an alkylene oxide in the presence of potassium hydroxide (KOH) as the catalyst. However, it is known that, when propylene oxide as the common alkylene oxide is used for addition polymerization in the presence of a KOH catalyst, a mono-ol having an unsaturated group at the molecular chain piece terminal is produced increasingly as the by-product, as the polyoxypropylene polyol increases in molecular weight.
In general, mono-ol content corresponds to overall degree of unsaturation of polyoxypropylene polyol. The mono-ol has a lower molecular weight than the polyoxypropylene polyol produced by the main reaction, and greatly widens molecular weight distribution of the polyoxypropylene polyol and hence decreases average number of functional groups. It is also known that the mono-ol retards formation of the polymer networks for the urethane-forming reaction with polyisocyanate compound, resulting in deterioration of mechanical strength of polyurethane as the reaction product.
Attempts have been made to improve productivity of the polyoxyalkylene polyol synthesis, while inhibiting formation of mono-ol as the by-product. For example, a double metal cyanide complex (DMC) is proposed as the catalyst for addition polymerization of propylene oxide, as disclosed by publications of U.S. Pat. No. 3,829,505 and U.S. Pat. No. 4,472,560, which describe that DMC is an excellent catalyst for polymerization of propylene oxide.
A publication of U.S. Pat. No. 5,728,745 discloses a polyoxyalkylene polyol synthesized in the presence of an improved DMC as the catalyst, which gives a microporous elastomer showing a very high green strength and demolded in a short time, without causing deterioration of the final elastomer properties. Japanese Patent Publication No. 3-47202 describes, in its exmaples, that the polyoxyalkylene polyol synthesized in the presence of a DMC catalyst gives a polyurethane-based resin for shoe soles highly resistant to moist heat.
However, addition polymerization of ethylene oxide as the alkylene oxide in the presence of a DMC catalyst needs several steps, e.g., deactivation of the DMC catalyst by the reaction with an oxidant (e.g., an oxygen-containing gas, peroxide or sulfate), separation of the residual catalyst from the polyoxyalkylene polyol, and addition polymerization in the presence of a hydroxide of alkali metal (e.g., KOH), alkoxide of alkali metal or the like as the catalyst, as disclosed by U.S. Pat. No. 5,235,114. The inventors of the present invention have synthesized a polyoxyalkylene polyol in the presence of a DMC catalyst, and produced the microcellular polyurethane elastomer from the polyol, to find that the microcellular polyurethane elastomer fails to satisfy the desired characteristics they have pursued with respect to demolding time, durability-related characteristics (e.g., compression set), and cell shape in a specific range.
One of the catalysts other than the above-described ones for synthesizing polyoxyalkylene polyol is a phosphazene compound, disclosed by a publication of EPO 763,555, Macromol. Rapid Commun. Vol. 17, pp. 143 to 148, 1996, and Macromol. Symp. Vol. 107, pp. 331 to 340, 1996). When used as the catalyst for synthesizing polyoxyalkylene polyol, the phosphazene compound brings about advantages of controlled production of the mono-ol as the by-product and greatly improved productivity.
It is an object of the present invention to provide a microcellular polyurethane elastomer which can solve the problems involved in the conventional techniques. It is another object of the present invention to provide a method of producing the same. More concretely, the present invention provides a microcellular polyurethane elastomer showing reduced demolding time, greatly reduced compression set and excellent mechanical properties, and, at the same time, excellent in appearances and coating characteristics, and also provides a method of producing the same.
The inventors of the present invention have found, after having extensively studied to develop a microcellular polyurethane elastomer of excellent characteristics and a method of efficiently producing the same, that the microcellular polyurethane elastomer can have excellent mechanical strength when it has an overall density (D) in a specific range and its compression set (CS2) and cell diameter on the skin surface satisfy specific correlations with its overall density (D), that the microcellular polyurethane elastomer can have excellent characteristics and its demolding time can be reduced to improve production efficiency by use of polyoxyalkylene polyol having a specific hydroxyl value (OHV), an overall degree of unsaturation and head-to-tail (H-T) linkage selectivity, and that the microcellular polyurethane elastomer can have reduced demolding time and excellent mechanical properties by use of a specific quantity of polyoxyalkylene polyol having a W20/W80 ratio as an index representing molecular weight distribution in a specific range, reaching the present invention.
The present invention, which solves the above problems, provides the following items (1) to (21).
(1) A microcellular polyurethane elastomer, having
(a) an overall density (D) of 100 kg/m3 or more but 900 kg/m3 or less,
(b) overall density (D) and compression set (CS2, unit: %) satisfying a relationship shown by the following equation (1)
CS2xe2x89xa60.00008*D2xe2x88x920.091*D+42 xe2x80x83xe2x80x83(1) 
xe2x80x83and having
overall density (D) and average cell diameter (X, unit: xcexcm) observed on the skin surface satisfying a relationship shown by the following equation (2):
Xxe2x89xa6120exe2x88x920.0015D xe2x80x83xe2x80x83(2). 
(2) The microcellular polyurethane elastomer of (1), wherein its overall density is 200 kg/m3 or more but 700 kg/m3or less.
(3) The microcellular polyurethane elastomer of (1), containing the cells having an average diameter of 1 xcexcm or more but 200 xcexcm or less.
(4) The microcellular polyurethane elastomer of one of (1) to (3), wherein its overall density and compression set satisfy a relationship shown by the following equation (3):
CS2xe2x89xa60.00008*D2xe2x88x920.091*D+40 xe2x80x83xe2x80x83(3). 
(5) The microcellular polyurethane elastomer of one of (1) to (3), wherein its average cell diameter (X, unit: xcexcm) observed on a skin surface satisfies the relationship shown by a following equation (4):
Xxe2x89xa6110e0.0015D xe2x80x83xe2x80x83(4). 
(6) A microcellular polyurethane elastomer a polyol with a polyisocyanate compound to having an overall density (D) of 100 kg/m3 or more but 900 kg/m3 or less obtained by reacting, wherein above described polyol contains 50 wt. % or more of at least one polyoxyalkylene polyol having a hydroxyl value of 2 to 200 mg-KOH/g, an overall degree of unsaturation of 0.001 to 0.07 meq./g and a head-to-tail linkage selectivity of 95 mol % or more for that of the polyoxyalkylene polyol produced by addition polymerization of propylene oxide.
(7) The microcellular polyurethane elastomer of (6), wherein above described polyoxyalkylene polyol is produced in the presence of a compound having a Pxe2x95x90N bond as a catalyst.
(8) The microcellular polyurethane elastomer of (1), obtained by reacting a polyol with a polyisocyanate compound, wherein above described polyol contains 50 wt. % or more of at least one polyoxyalkylene polyol having a hydroxyl value of 2 to 200 mg-KOH/g, an overall degree of unsaturation of 0.001 to 0.07 meq./g and a head-to-tail linkage selectivity of 95 mol % or more for that of the polyoxyalkylene polyol produced by addition polymerization of propylene oxide.
(9) The microcellular polyurethane elastomer of (8), wherein above described polyoxyalkylene polyol is produced in the presence of a compound having a Pxe2x95x90N bond as a catalyst.
(10) The microcellular polyurethane elastomer of (8), wherein above described polyol contains 0.5 to 50 wt. % of polymer-dispersed polyol containing 1 to 50 wt. % of the polymer micro particles produced by polymerization of at least one monomer containing an ethylenically unsaturated group.
(11) The microcellular polyurethane elastomer of (10), wherein above described polymer-dispersed polyol is produced by polymerization of at least one monomer containing an ethylenically unsaturated group in at least one polyoxyalkylene polyol having a hydroxyl value of 2 to 200 mg-KOH/g, an overall degree of unsaturation of 0.001 to 0.07 meq./g and a head-to-tail linkage selectivity of 95 mol % or more for that of the polyoxyalkylene polyol produced by addition polymerization of propylene oxide.
(12) The microcellular polyurethane elastomer of (10), wherein above described polymer-dispersed polyol contains 10 to 45 wt. % of above described polymer micro particles.
(13) The microcellular polyurethane elastomer of one of (10) to (12), wherein above described monomer containing an ethylenically unsaturated group is one or more types of monomers selected from the group consisting of acrylonitrile, styrene, acrylamide and methyl methacrylate.
(14) The microcellular polyurethane elastomer of one of (10) to (13), wherein above described monomer containing an ethylenically unsaturated group contains 30 wt. % or more of styrene.
(15) The microcellular polyurethane elastomer of one of (1) to (14), which is obtained by reacting an isocyanate-terminated prepolymer with a polyol, above described prepolymer being obtained by reacting an aromatic polyester polyol with a polyisocyanate.
(16) A shoe sole which is made of the microcellular polyurethane elastomer of one of (1) to (15).
(17) A method of producing a microcellular polyurethane elastomer, obtained by reacting a polyol with a polyisocyanate compound to have
(a) an overall density (D) of 100 kg/m3 or more but 900 kg/m3 or less, and
(b) overall density (D) and compression set (CS2, unit: %) satisfying the relationship shown by the following equation (1): and
CS2xe2x89xa60.00008*D2xe2x88x920.091*D+42 xe2x80x83xe2x80x83(1) 
xe2x80x83and to have overall density (D) and average cell diameter (X, unit: xcexcm) observed on the skin surface satisfying the relationship shown by the following equation (2):
Xxe2x89xa6120exe2x88x920.0015D xe2x80x83xe2x80x83(2) 
xe2x80x83wherein, above described polyol contains 50 wt. % or more of at least one polyoxyalkylene polyol having a hydroxyl value of 2 to 200 mg-KOH/g, an overall degree of unsaturation of 0.001 to 0.07 meq./g and a head-to-tail linkage selectivity of 95 mol % or more for that of the polyoxyalkylene polyol produced by addition polymerization of propylene oxide.
(18) The method of producing a finely foamed polyurethane elastmer of (17), wherein above described polyoxyalkylene polyol is produced in the presence of a compound having a Pxe2x95x90N bond as a catalyst.
(19) The method of producing a finely foamed polyurethane elastmer of (17), which is obtained by reacting a polyol with a polyisocyanate compound, wherein above described polyol contains 0.5 to 50 wt. % of polymer-dispersed polyol containing 1 to 50 wt. % of the polymer micro particles produced by polymerization of at least one monomer containing an ethylenically unsaturated group.
(20) The method of producing a finely foamed polyurethane elastmer of one of (17) to (19), which is obtained by reacting a polyol with a polyisocyanate compound, wherein above described polyisocyanate compound is an isocyanate-terminated prepolymer obtained by reacting an aromatic polyester polyol with a polyisocyanate.
(21) The method of producing a finely foamed polyurethane elastmer of (20), wherein above described polyisocyanate compound contains 20 wt. % or more of the isocyanate-terminated prepolymer obtained by reacting an aromatic polyester polyol with a polyisocyanate.
The present invention will be described in detail below by the preferred embodiments.
Microcellular polyurethane elastomer
The microcellular polyurethane elastomer has an overall density of 100 to 900 kg/m3, preferably 200 to 800 kg/m3, more preferably 200 to 700 kg/m3, wherein overall density means density of the whole elastomer including its surface layer section. Keeping overall density at 100 kg/m3 or more gives the elastomer of improved mechanical strength and allows the formed elastomer to exhibit excellent mechanical properties. The microcellular polyurethane elastomer of the present invention has following mechanical properties; hardness (Asker C): 5 to 95, tensile strength (TB): 0.5 to 20 MPa, maximum elongation (EB): 100 to 700%, tear strength (TR): 0.5 to 50 kN/m, and compression set (CS2): 3 to 35%, which vary depending on its overall density.
Compression set (CS2) is an important property for the microcellular polyurethane elastomer, especially for shoe soles, because it determines the product quality. The elastomer of lower CS2 value suffers less dimensional changes when used repeatedly, and enables to keep desired elastic feeling for extended periods. It is determined in accordance with JIS K-6262, where the circular specimen 29 mm in diameter, cut from a sheet, was tested under the conditions of test temperature: 50xc2x11xc2x0 C., test time: 6 hours, and compression ratio: 50%. The compression set thus determined is referred to as the xe2x80x9cCS2xe2x80x9d value in this specification.
The CS2 value of the microcellular polyurethane elastomer of the present invention satisfies the relationship shown by the following equation (1):
CS2xe2x89xa60.00008*D2xe2x88x920.091*D+42 xe2x80x83xe2x80x83(1) 
preferably the following equation (3):
CS2xe2x89xa60.00008*D2xe2x88x920.091*D+40 xe2x80x83xe2x80x83(3) 
more preferably the following equation (5): and
CS2xe2x89xa60.00008*D2xe2x88x920.091*D+38 xe2x80x83xe2x80x83(5) 
especially preferably the following equation (6):
CS2xe2x89xa635*exe2x88x920.0025*D xe2x80x83xe2x80x83(6). 
The microcellular polyurethane elastomer should have sufficient mechanical strength, when it has a CS2 value in the above range.
Surface characteristics are also important for the foamed polyurethane elastomer for shoe soles. It is needless to say that surface characteristics greatly affect quality of the uncoated product, let alone coated surface of the product post-treated by coating. It is preferable that the microcellular polyurethane elastomer has a glossy surface without defects, e.g., flow marks and pinholes, before being coated, and keeps the glossy surface without defects, e.g., uneven coloration, after being coated.
The inventors of the present invention have found that the surface characteristics are determined by size of the cells on the skin surface, where the skin surface of the present invention means the surface of the microcellular polyurethane elastomer sheet in contact with the mold, e.g., of aluminum 12.5 by 150.0 by 250.0 mm in inner dimensions, in which it is formed. The surface (150.0 by 250.0 mm) in contact with the mold bottom was observed for its cell diameters by a microcamera at a total of five position, the four corners and center, for the portion excluding the 20 mm wide sections from the edges in the length and breadth directions. The average diameter of these cells at each of the 5 points is determined by image processor/analyzer, and the average cell diameter X on the skin surface is determined by averaging the average diameters at these points.
The cell diameter (X, unit: xcexcm) observed on the skin surface of the microcellular polyurethane elastomer of the present invention preferably satisfies the relationship shown by the following equation (2):
Xxe2x89xa6120e0.0015D xe2x80x83xe2x80x83(2) 
more preferably the following equation (4): and
Xxe2x89xa6110e0.0015D xe2x80x83xe2x80x83(4) 
still more preferably the following equation (7):
Xxe2x89xa6100e0.0015D xe2x80x83xe2x80x83(7) 
Controlling the average cell diameter on the skin surface in the above range substantially increases thickness of the skin layer. The inventors of the present invention have also found that increasing thickness of the skin layer improves mechanical properties, e.g., tensile strength, of the elastomer.
The average cell diameter inside of the microcellular polyurethane elastomer of (e.g. the average cell diameter as measured without skin layer) the present invention is preferably 1 xcexcm or more but 200 xcexcm or less, more preferably 1 xcexcm or more but 150 xcexcm or less, still more preferably 1 xcexcm or more but 100 xcexcm or less, and most preferably 5 xcexcm or more but 100 xcexcm or less. The average cell diameter inside of the microcellular polyurethane elastomer of the present invention is determined by observing diameters of the cells at the four planes of the specimen in the sectional direction (perpendicular to the skin surface) by a microcamera, and finding the average cell diameter by an image processor/analyzer, where the specimen is prepared by, e.g., cutting the sheet of microcellular polyurethane elastomer, formed in an aluminum mold of 12.5 by 150.0 by 250.0 mm in inner dimensions, into a shape of 3 cm in the length direction and 1 cm in the breadth direction from the central portion, and removing the 4 mm thick upper and lower sections.
Keeping the average cell diameter at 200 xcexcm or less, especially 100 xcexcm or less, can inhibit growth of the cell diameter, and give the microcellular polyurethane elastomer of good feeling of touch and improved mechanical properties.
Production of microcellular polyurethane elastomer
The microcellular polyurethane elastomer of the present invention, having the above-described characteristics, is produced by reacting a polyol including a polyoxyalkylene polyol having a specific structure as the main component, with a polyisocyanate compound in the presence of a foaming agent, catalyst and foam stabilizer. Each component is described first in detail.
Polyol
The polyol for the present invention contains 50 wt. % or more of at least one polyoxyalkylene polyol having a hydroxyl value (OHV) of 2 to 200 mg-KOH/g, an overall degree of unsaturation of 0.001 to 0.07 meq./g, and head-to-tail (H-T) linkage selectivity of 95 mol % or more for that of the polyoxyalkylene polyol produced by addition polymerization of propylene oxide.
Polyoxyalkylene polyol
The polyoxyalkylene polyol for the present invention has an OHV value of 2 to 200 mg-KOH/g, preferably 9 to 120 mg-KOH/g, more preferably 10 to 100 mg-KOH/g, still more preferably 20 to 80 mg-KOH/g, and most preferably 20 to 60 mg-KOH/g, viewed from mechanical properties and demolding characteristics of the microcellular polyurethane elastomer.
The polyoxyalkylene polyol for the present invention also has an overall degree of unsaturation of 0.07 meq./g or less, preferably 0.05 meq./g or less, more preferably 0.04 meq./g or less, and most preferably 0.03 meq./g or less, in order to improve mechanical strength of the microcellular polyurethane elastomer and allow it to exhibit its inherent properties in the early stage.
Keeping an overall degree of unsaturation at 0.07 meq./g or less greatly improves mechanical strength of the microcellular polyurethane elastomer. The lower limit of an overall degree of unsaturation is not limited for the present invention, but around 0.001 meq./g.
The polyoxyalkylene polyol for the present invention also has a head-to-tail (H-T) linkage selectivity of 95 mol % or more, preferably 96 mol % or more, more preferably 97 mol % or more, where the selectivity results from the cleavage mode of oxirane ring in addition polymerization of propylene oxide. Keeping head-to-tail (H-T) linkage selectivity at 95 mol % or more can keep polyoxyalkylene polyol viscosity in an adequate range, develop the compatibility with an aid/additive, e.g., foam stabilizer, and also inhibit growth of the average cell diameter and deterioration of processability of the microcellular polyurethane elastomer.
The polyoxyalkylene polyol for the present invention also has a W20/W80 ratio of 1.5 or more but below 3.0, where W20 and W80 are widths of the peaks at 20 and 80% of the highest peak in the gel permeation chromatography (GPC) elution curve.
The causes for broadening the molecular weight distribution of polyoxyalkylene polyol include formation of mono-ol by the side-reaction of propylene oxide, and formation of a high-molecular-weight component as the by-product. The mono-ol (corresponding to an overall degree of unsaturation, defined in this specification) has a lower molecular weight than the polyoxyalkylene polyol produced by the main reaction, and slower than the component formed by the main reaction in peak holding time in the GPC elution curve. Decreasing concentration of mono-ol makes an overall degree of unsaturation of the polyol decrease, as a result, mechanical strength of the microcellular polyurethane elastomer is greatly improved.
Therefore, a polyoxyalkylene polyol containing a higher proportion of the high-molecular-weight component has a higher viscosity than the one containing a lower proportion of the high-molecular-weight component, increasing viscosity of the resin premix containing a catalyst, foam stabilizer, foaming agent or the like and also viscosity of the isocyanate-terminated prepolymer obtained by the reaction with a polyisocyanate, and hence causing problems, e.g., deteriorated processability and flowability of the microcellular polyurethane elastomer, to deteriorate its formability and grow its cell diameter.
The polyoxyalkylene polyol for the present invention is preferably produced from propylene oxide as the main monomer and ethylene oxide. Introduction of ethylene oxide into the terminal of the polyoxyalkylene polyol structure with the propylene oxide as the main chain allows the polyol to exhibit a sufficient reaction rate, and also can sufficiently increase molecular weight of the microcellular polyurethane elastomer. Content of ethylene oxide in the polyoxyalkylene polyol for the present invention is preferably 30 wt. % or less, more preferably 5 to 30 wt. %, and most preferably 10 to 25 wt. %. Rate for producing a primary hydroxyl group at the terminal of the polyoxyalkylene polyol is preferably around 50 mol % or more, more preferably 70 mol % or more, still more preferably 75 mol % or more, and most preferably 80 mol % or more.
It is also preferable that the polyoxyalkylene polyol for the present invention is produced in the presence of a compound having the Pxe2x95x90N bond as a catalyst. More preferably, the compound is one or more types of compound selected from the group consisting of phosphazenium compound, phosphazene compound and phosphine oxide compound, of which a phosphazenium compound is most preferable. The polyoxyalkylene polyol produced in the presence of a phosphazenium compound preferably has a hydroxyl value of 2 to 200 mg-KOH/g, an overall degree of unsaturation of 0.001 to 0.07 meq./g and a head-to-tail linkage selectivity of 95 mol % or more for that of the polyoxyalkylene polyol produced by addition polymerization of propylene oxide. Although the polyoxyalkylene polyol is preferably produced in the presence of a phosphazenium compound, a hydroxide of alkali metal, e.g., cesium hydroxide (CsOH), may be used in combination with the phosphazenium compound, so long as the effects of the present invention are not damaged. The catalyst for producing the polyoxyalkylene polyol will be described in detail later.
A polyol having a structure other than the above polyoxyalkylene polyol may be used for production of the microcellular polyurethane elastomer of the present invention. The polyoxyalkylene polyol for the present invention accounts for 50 wt. % or more of the polyols, preferably 70 wt. % or more and more preferably 80 wt. % or more. The polyol, other than the polyoxyalkylene polyol, which can be used for the present invention, will be described in detail later.
The polyoxyalkylene polyol preferably has a number-average molecular weight of 1,000 to 12,000 for the microcellular polyurethane elastomer for shoe soles. More preferably, it has a number-average molecular weight of 2,000 to 8,000, and ethylene oxide added to its terminals.
Production of polyoxyalkylene polyol
The polyoxyalkylene polyol for the present invention is also referred to as polyoxyalkylene polyether polyol, which is an oligomer or polymer produced by ring opening polymerization of an alkylene oxide in the presence of a catalyst and active hydrogen compound as the initiator. One or more types of initiators and alkylene oxides may be used for the present invention.
Catalyst for producing polyoxyalkylene polyol
The catalyst for producing polyoxyalkylene polyol for the present invention is particularly preferably a compound having the Pxe2x95x90N bond in its molecular structure. The example of such a compound is one or more types of compound selected from the group consisting of phosphazenium compound, phosphazene compound and phosphine oxide compound.
The preferable phosphazenium compounds are a salt of hosphazenium cation and inorganic anion, represented by the chemical formula (1), disclosed by Japanese Patent Application Laid-Open No. 11-106500, 
and phosphazenium compound, represented by the chemical formula (2): 
where, (a), (b), (c) and (d) in the chemical formulas (1) and (2) are each an integer of 0 to 3, which are not simultaneously zero; R in the chemical formulas (1) and (2) is a hydrocarbon group of 1 to 10 carbon atoms, which may be the same or different, wherein two Rs on the same nitrogen atom may form a ring structure; (r) in the chemical formula (1) is an integer of 1 to 3, and representing number of phosphazenium cation; Tr in the chemical formula (1) represents an inorganic anion having a valence number of (r); and Qxe2x88x92 in the Equation (2) represents hydroxy anion, alkoxy anion, aryloxy anion or carboxy anion, more concretely,
tetrakis[tris(dimethylamino)phosphoranilideneamino] phosphonium hydroxide, tetrakis[tris(dimethylamino) phosphoranilideneamino]phosphonium methoxide, tetrakis [tris(dimethylamino)phosphoranilideneamino]phosphonium ethoxide, tetrakis[tri(pyrrolidin-1-yl) phosphoranilideneamino]phosphonium tert-butoxide, or the like.
The phosphazene compounds useful for the present invention are disclosed by EP-763555, e.g.,
1-tert-butyl-2,2,2-tris(dimethylamino)phosphazene,
1-(1,1,3,3-tetramethylbutyl)-2,2,2-tris(dimethylamino)pho sphazene,
1-ethyl-2,2,4,4,4-pentakis(dimethylamino)-2xcex5,4xcex5-catenad i(phosphazene),
1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimet hylamino)
phosphoranilideneamino]-2xcex5,4xcex5-catenadi(phosphazene),
1-(1,1,3,3-tetramethylbutyl)-4,4,4-tris(dimethylamino)-2, 2-bis[tris(dimethylamino)phosphoranilideneamino]-2xcex5,4xcex5-catenadi(phosphazene),
1-tert-butyl-2,2,2-tri(1-pyrrolidinyl) phosphazene, and
7-ethyl-5,11-dimethyl-1,5,7,11-tetraaza-6xcex5-phosphaspiro[5,5]undeca-1(6)-ene.
The phosphine oxide compounds useful for the present invention are disclosed by Japanese Patent Application No. 11-296610, e.g.,
tris[tris(dimethylamino)phosphoranilideneamino]phosphine oxide, and
tris[tris(dimethylamino)phosphoranilideneamino]phosphine oxide.
Of the above compounds having the Pxe2x95x90N bond, preferable ones are phosphazenium compounds and phosfine compounds, and more preferable ones are phosphazenium compounds.
Initiator
The active hydrogen compounds useful as the initiator for producing polyoxyalkylene polyol include those having an activated hydrogen atom on the oxygen or nitrogen atom.
Of the active hydrogen compounds described below, more preferable ones include ethylene glycol, propylene glycol, dipropylene glycol, glycerin, trimethylolpropane, pentaerythritol, sorbitol, and sucrose.
(1) Active hydrogen compounds having an activated hydrogen atom on oxygen atom
The active hydrogen compounds useful for the present invention and having an activated hydrogen atom on the oxygen atom include water, polyvalent carboxylic acids having a carboxyl group, carbamic acid, polyhydric alcohols having a hydroxyl group, sucrose and its derivatives, and aromatic compounds having a hydroxyl group.
The polyvalent carboxylic acids having a carboxyl group include malonic acid, succinic acid, maleic acid, fumaric acid, adipic acid, itaconic acid, butanetetracarboxylic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, and pyromellitic acid.
The carbamic acids include N,N-diethyl carbamate, N-carboxypyrrolidone, N-carboxyaniline and N,Nxe2x80x2-dicarboxy-2,4-toluenediamine.
The polyhydric alcohols having a hydroxyl group include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanediol, trimethylolpropane, glycerin, diglycerin, pentaerythritol and dipentaerythritol.
The saccharides and their derivatives include glucose, sorbitol, dextrose, fructose and sucrose.
The aromatic compounds having a hydroxyl group include 2-naphthol, 2, 6-dihydroxynaphthalene, bisphenol A, bisphenol F, hydroquinone, resorcin, and bis(hydroxyethyl)terephthalate.
(2) Active hydrogen compounds having an activated hydrogen atom on nitrogen atom
The active hydrogen compounds useful for the present invention and having an activated hydrogen atom on the nitrogen atom include aliphatic and aromatic amines.
The aliphatic and aromatic amines include n-propylamine, isopropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, cyclohexylamine, benzylamine, xcex2-phenylethylamine, aniline, o-toluidine, m-toluidine, and p-toluidine.
The polyvalent amines include ethylenediamine, di(2-aminoethyl)amine, hexamethylenediamine, 4,4xe2x80x2-diaminodiphenylmethane, tri(2-aminoethyl)amine, N,Nxe2x80x2-dimethylethylenediamine, N,Nxe2x80x2-diethylethylendiamine, and di(2-methylaminoethyl)amine.
Alkylene oxide
The alkylene oxide useful for producing polyoxyalkylene polyol for the present invention preferably has propylene oxide as the main component, and is more preferably a mixture of 50 wt. % or more of propylene oxide and one or more other alkylene oxide compounds. Use of this quantity of propylene oxide allows to control oxypropylene group content in the polyoxyalkylene polyol at 50 wt. % or more. The polyoxyalkylene polyol has a sufficiently low viscosity, when its oxypropylene group content is controlled at 50 wt. % or more to give a resin premix of good flowability. The alkylene oxide compounds which can be used in combination with propylene oxide include epoxy compounds, e.g., ethylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, styrene oxide, cyclohexene oxide, epichlorohydrin, epibromohydrin, methyl glycidyl ether, aryl glycidyl ether, and phenyl glycidyl ether.
Of these, ethylene oxide is more preferable to be used in combination with propylene oxide.
Other polyols
A polyol having a structure other than the above polyoxyalkylene polyol may be used for production of the microcellular polyurethane elastomer of the present invention, so long as it does not damage the effects of the present invention. Such polyols useful for the present invention include di- to hexa-valent polyhydric alcohols, polyester polyols (including polyester polyols, aromatic polyester polyols and polycaprolactone polyols for common purposes), polycarbonate polyols, and polymer-dispersed polyols.
(Polyhydric alcohol)
The polyhydric alcohols include di-valent alcohol, e.g., 1,3-propanediol, 1,4-butanediol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, pentanediol, hexanediol, cyclohexanediol and neopentyl glycol; tri-valent alcohols, e.g., glycerin, trimethylolethane and trimethylolpropane; tetra-valent alcohols, e.g., pentaerythritol and diglycerin; and hexa-valent alcohols, e.g., sorbitol.
(Polyester polyol for common purposes)
The polyester polyol for common purposes includes polyester polyol produced by polycondensation of a dicarboxylic acid and polyhydric alcohol. The dicarboxylic acids for producing the polyester polyols include adipic acid, succinic acid, azelac acid, suberic acid and ricinolic acid. The polyhydric alcohols include ethylene glycol, propylene glycol, butanediol, hexanediol, neopentylglycol, diethylene glycol, triethylene glycol, pentanediol, cyclohexanediol, polyoxyalkylene polyol, polytetramethylene ether glycol, glycerin, trimethylolpropane, trimethylolethane and pentaerythritol.
(Polycaprolactone polyol)
The polycaprolactone polyol is a polyol from xcex5-caprolactone and polyhydric alcohol. These polyols have, in general, a number-average molecular weight of 500 to 4,000 and hydroxyl value of around 30 to 240 mg-KOH/g. The polyhydric alcohols for the above polyester polyols may be used for producing the polycaprolactone polyols.
(Polycarbonate polyol)
The polycarbonate polyols are liner chain aliphatic or alicyclic polyols produced by condensation of a polyhydric alcohol (e.g., 1,4-butanediol and 1,6-hexanediol) and dimethyl or diethyl carbonate, and shown by the following general formula (3): 
where, R1 and R2 are each an aliphatic alkylene or alicyclic alkylene group, and may be the same or different.
They have, in general, a hydroxyl value of around 60 to 200 mg-KOH/g.
(Aromatic polyester polyol)
The aromatic polyester polyols are produced by the interesterification between synthetic resin, e.g., polyethylene terephthalate, and polyhydric alcohol, or polycondensation of an aromatic carboxylic acid (e.g., o-, m- or p-phthalic acid) and polyhydric alcohol. The preferable polyhydric alcohols for the above purpose include polyoxyalkylene polyols and polytetramethylene ether glycols, in addition to the above-described polyhydric alcohols. They may be used either alone or in combination. The aromatic ester polyol preferably has a hydroxyl value of 10 to 150 mg-KOH/g, more preferably 15 to 100 mg-KOH/g and acid value of 0.7 mg-KOH/g or less, more preferably 0.5 mg-KOH/g or less. Use of the aromatic polyester polyol as the polyol of isocyanate-terminated prepolymer helps improve mechanical properties of the microcellular polyurethane elastomer.
(Polymer-dispersed polyol)
The polymer-dispersed polyol means the one dispersed with the vinyl polymer particles (hereinafter sometimes referred to as simply the polymer micro particles) partly containing the graft polymer, produced by dispersion polymerization of at least one monomer containing ethylenically unsaturated group (e.g., acrilonitrile and styrene) in a polyol in the presence of a radical initiator (e.g., azobisisobutylonitrile). Use of the polymer-dispersed polyol brings about the effect of sufficiently increasing hardness of the microcellular polyurethane elastomer.
The polyols useful for the present invention include polyester polyols and polyoxyalkylene polyols having 2 to 6 functional groups on the average, the above-described polyoxyalkylene polyols having specific properties for the present invention being more preferable. The polymer produced by the dispersion polymerization preferably has an average particle size of 0.1 to 10 xcexcm.
The polymer-dispersed polyol preferably has a hydroxyl value of 5 to 99 mg-KOH/g, more preferably 10 to 59 mg-KOH/g, for the microcellular polyurethane elastomer to exhibit sufficiently high mechanical strength.
The polymer-dispersed polyol for the present invention preferably contains the polymer micro particles at 1 to 50 wt. %, based on the polyoxyalkylene polyol, more preferably 10 to 45 wt. %. The monomer containing an ethylenically unsaturated group is preferably one or more types selected from the group consisting of acrylonitrile, styrene, acrylamide and methyl methacrylate. Use of the monomer containing an ethylenically unsaturated group, selected from the above group, for the polymer-dispersed polyol helps improve mechanical properties of the microcellular polyurethane elastomer. It is particularly preferable to use the polymer-dispersed polyol containing styrene at 30 wt. % or more, still more preferably 40 wt. % or more, and most preferably 50 wt. % or more. When the polymer micro particles based on an acrylonitrile/styrene copolymer are used for the polymer-dispersed polyol, whiteness of the microcellular polyurethane elastomer is affected by styrene content. Controlling styrene content helps produce the microcellular polyurethane elastomer of white appearances suitable for white-colored shoe soles.
Polyisocyanate compound
Any polyisocyanate compound which is used for production of polyurethane may be used for production of the microcellular polyurethane elastomer of the present invention.
The polyisocyanate compounds useful for the present invention include diisocyanates, e.g., tolylene diisocyanate (including various types of mixtures of the isomers), diphenylmethane diisocyanate (including various types of mixtures of the isomers), 3,3xe2x80x2-dimethyl-4,4xe2x80x2-biphenylene diisocyanate, norbornane diisocyanate, 1,4-phenylene diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, dicyclohexylmethane-4,4xe2x80x2-diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated xylene diisocyanate, 1,4-cyclohexyl diisocyanate, 1-methyl-2,4-diisocyanate cyclohexane and 2,4,4-trimethyl-1,6-diisocyanate-hexane; and triisocyanates, e.g., 4,4xe2x80x2,4xe2x80x3-triphenylmethane triisocyanate and tris(4-phenylisocyanate)thiophosphate.
The other isocyanates useful for the present invention include the above-described polyisocyanates modified with urethane, isocyanurate, carbodiimide or burette; and multifunctional isocyanates, e.g., crude tolylene diisocyanate, polymethylene isocyanate and polyphenyl isocyanate.
Of these, the polyisocyanate or carbodiimide-modified polyisocyanate is preferable for production of the suitable urethane-modified isocyanate-terminated prepolymer by the reaction with polyol.
The isocyanate-terminated prepolymer molecule contains the isocyanate group at 0.3 to 30 wt. % (as isocyanate group content in the isocyanate-terminated prepolymer), preferably 1 to 30 wt. %, more preferably 4 to 25 wt. %, most preferably 5 to 25 wt. %.
The polyol for production of the isocyanate-terminated prepolymer is not limited. Some examples include polyoxyalkylene polyol, polyester polyol, polybutadiene polyol and polycarbonate polyol. They may be used either alone or in combination.
Particularly preferable one is an aromatic polyester polyol or the polyoxyalkylene polyol for the present invention, which is reacted with a polyisocyanate to produce the urethane-modified isocyanate-terminated prepolymer.
Especially, use of an aromatic polyester polyol as the polyol for the isocyanate-terminated prepolymer increases content of the isocyanate-terminated prepolymer from the aromatic polyester polyol and polyisocyanate to 20 wt. % or more, preferably 30 wt. % or more, more preferably 40 wt. % or more, increasing its reactivity and hence giving the microcellular polyurethane elastomer of excellent mechanical strength.
Foaming agent
The foaming agents useful for production of the microcellular polyurethane elastomer of the present invention include water, cyclopentane, trichloromethane, trichloromonofluoromethane, 1,1,2-trichlorotrifluoromethane, 1,1-dichloro-2,2,2-trifluoroethane, and 1,1-dichloro-1-monofluoroethane. They may be used either alone or in combination. Of these, the more preferable one is water used alone.
Catalyst
Various known catalysts may be used for the present invention. They include amines, e.g., triethylamine, tripropylamine, tributylamine, morpholine, N-methylmorpholine, N-ethylmorpholine, dimethylcyclohexylamine, 1,4-diazabicyclo-(2,2,2)-octane (hereinafter referred to as TEDA), TEDA salt, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylhexamethylenediamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylpropylenediamine, N,N,Nxe2x80x2,Nxe2x80x2,Nxe2x80x3-pentamethyldiethylenetriamine, trimethylaminoethylpiperazine, N,N-dimethylcyclohexylamine, N,N-dimethylbenzylamine, N-methylmorpholine, N-ethylmorpholine, bis(dimethylaminoalkyl)piperazine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylethylenediamine, N,N-diethylbenzylamine, bis(N,N-diethylaminoethyl)adipate, N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,3-butanediamine, N,N-dimethyl-xcex2-phenylethylamine, 1,2-dimethylimidazole, and 2-methylimidazole; organotin compounds, e.g., tin octylate, tin oleate, tin laurate, dibutyltin diacetate and dibutyltin dilaurate; and organolead compounds, e.g., lead octylate and lead naphthenate. They may be used either alone or in combination, preferably at 0.1 to 10 wt. parts per 100 wt. parts of the polyol, more preferably 0.1 to 5 wt. parts.
Chain extender
The suitable chain extender is a polyol having a low molecular weight of 400 or less. These compounds include propylene glycol, dipropylene glycol, ethylene glycol, diethylene glycol, 1,4-butanediol, 1,3-butanediol, neopentyl glycol, 1,6-hexanediol, glycerin, bishydroxyethoxy benzene, bishydroxyethyl terephthalate and diethoxy resorcin. Two or more types of the chain extenders may be used. The preferable extenders are ethylene glycol and 1,4-butanediol. It is preferable to use the chain extender at 3 to 60 wt. parts per 100 wt. parts of the polyol, more preferably 3 to 50 wt. parts.
Foam stabilizer
The foam stabilizer for the present invention is not limited, so long as it is generally used for production of polyurethane foams, and known organosilicon-based surfactants may be used. The amount used is preferably at 0.1 to 20 wt. parts per 100 wt. parts of the polyol, more preferably at 0.2 to 5 wt. parts. The examples of the stabilizers include SRX-274C, SF-2969, SE-2961 and SF-2962 (Trade Name, produced by Toray/Dow Corning Silicone); L-5309, L-5302, L-3601, L-5307 and L-3600 (Trade Name, produced by NIPPON UNICAR COMPANY LTD.).
Other additives
The other additives useful for the present invention include a yellowing inhibitor, ultraviolet ray absorber, antioxidant, flame retardant and colorant.
Method of producing the microcellular polyurethane elastomer
The microcellular polyurethane elastomer of the present invention is produced by mixing, under agitation, a resin premix with a polyisocyanate compound, wherein the resin premix is a mixture of the polyol for the present invention (including polyoxyalkylene polyol), and additives, e.g., chain extender, water as the foaming agent, catalyst and foaming agent, which is prepared beforehand. It is preferable to keep an NOC index normally at 0.8 to 1.3, more preferably 0.9 to 1.2, wherein NOC index is a ratio of moles of the active hydrogen in the total active hydrogen compounds (polyol, chain extender and water as the foaming agent) to moles of the isocyanate group in the polyisocyanate compound.
The mixing with agitation is effected normally by a low- or high-pressure circulation type foaming machine at 20 to 60xc2x0 C., although varying depending on size of the molded product of the microcellular polyurethane elastomer. When a low-pressure foaming machine is used in an open mold, for example, the mixture of the resin premix and polyisocyanate compound is injected into the mold, the open mold is quickly closed by a clamp, and the mixture is cured at 70xc2x0 C. for 5 to 20 min by, e.g., hot wind in a drier.
When cured, the microcellular polyurethane elastomer is withdrawn from the mold, to analyze its properties. The after cure, when required, is effected normally under the conditions of, e.g., 70xc2x0 C. for 24 or 2 hours.
The microcellular polyurethane elastomer is normally incorporated with 0.1 to 5 wt. parts of water as the foaming agent, 0.1 to 20 wt. parts of a foam stabilizer, 0.1 to 10 wt. parts of a catalyst for forming urethane and 3 to 60 wt. parts of a chain extender, all per 100 wt. parts of the polyol, in order to satisfy the above required characteristics.
 less than  less than Applications of the microcellular polyurethane elastomer greater than  greater than 
The microcellular polyurethane elastomer of the present invention is excellent in mechanical properties, e.g., tensile strength, 100% modulus, maximum elongation, tear strength and compression set, and also excellent in productivity coming from its reduced demolding time. The shoe sole of the microcellular polyurethane elastomer of these characteristics provides good feeling when the shoe on the sole is worn and is excellent in durability. Controlling cell diameter on the skin surface in a specific range keeps good surface and coating characteristics. Therefore, the microcellular polyurethane elastomer of the present invention can suitably find various applications, including shoe soles, gaskets for electric appliances, gaskets for industrial parts, seat mats and foot mats, vibration and sound insulators, and shock absorbers.
The present invention provides a microcellular polyurethane elastomer, excellent in mechanical properties, e.g., tensile strength, 100% modulus, maximum elongation, tear strength and compression set, and suitable for, e.g., shoe soles of excellent surface and coating characteristics. The microcellular polyurethane elastomer of the present invention, with its excellent mechanical properties, can be lower in density than the conventional elastomer of the equivalent mechanical properties, and can reduce weight of the products for various purposes.
In particular, a microcellular polyurethane elastomer retaining excellent mechanical properties can be obtained even with a reduced demolding time.
The shoe sole or the like of such a polyurethane elastomer provides good feeling when the shoe on the sole is worn and is excellent in durability and surface characteristics.